FIG. 1A illustrates a simplified diagram of an exemplary test system 100 for testing an electronic device 110. Tester 102 generates test data, which is written through communications link 106 to interface apparatus 108, which provides connections (not shown) to probes 112 that, as shown in FIG. 1A, contact terminals 114 of the electronic device 110 under test. Response data generated by the electronic device 110 returns to the tester 102 through probes 112, interface apparatus 108, and communication link 106. The communications link 106, interface apparatus 108, and probes 112 thus provide a plurality of communications channels between the tester 102 and the electronic device 110 under test. Of course, other devices may be included in the system 100. For example, devices for processing and/or routing test data and response data may be placed between the communications link 106 and the interface apparatus 108.
The interface apparatus 108 can be a probe card apparatus, for contacting an electronic device 110 under test. Typically, power must be supplied to the electronic device 110. As shown in FIG. 1A, the power supply 104 is part of the tester 102, and power from the power supply 104 is supplied through one of the communications channels formed by the communications link 106, interface apparatus 108, and power probe 116 to the power terminal 118 of the electronic device 110.
FIG. 1B illustrates a schematic diagram of a single power line 120 from the power supply 104 to the power terminal 118 of the electronic device 110 being tested. Power line 120 represents one communications channel from the tester 102 to the electronic device being tested 110 and thus comprises a portion of the communications link 106, the interface apparatus 108, and the power probe 116. As shown in FIG. 1B, a by-pass capacitor 122 is often connected between the power line 120 and ground 124 to filter noise on the power line 120.
At times, the electronic device 110 being tested has a fault in which power is shorted to ground in the electronic device 110. Such a condition typically causes a large current surge from the power supply 104. Even if power supply 104 can include over-current protection that automatically shuts power supply 104 off upon detection of such a fault, the over-current protection circuitry (not shown) in the power supply 104 may be unable to turn the power supply 104 off due to both the delay and inductance of the power line 120 before a current surge travels down power line 120. If sufficiently large, such a current surge can damage the interface apparatus 108 or a power probe 116. In fact, probe 116 may be particularly susceptible to such damage. Moreover, even if the over-current protection circuitry (not shown) in power supply 104 is able to shut the power supply 104 off in time to prevent a current surge, by-pass capacitor 122 is likely to discharge rapidly, and the resulting current through power probe 116 may damage the probe 116.